At the 2006 UCI Track Cycling World Championships, Bos won the keirin and completed a triple, having been world champion in the sprint, kilo and keirin . He won the keirin after accelerating with two laps to go, winning by a wide margin and able to raise his hands and salute the crowd as he passed the finish line.[3] His French rival, and bronze medal winner, Arnaud Tournant, said Bos' performance was "the best I’ve seen in a very long time."

On 16 December 2006, Bos broke the world 200m track record during qualification rounds for the sprint at a World Cup meeting in Moscow. Bos clocked 9.772 seconds (after a computer initially had given him an unlikely 9.086 seconds) and beat the 11-year record held by CanadianCurt Harnett. Bos declared the 200m the "ultimate record" for track cyclists.[4] Five days later Bos was elected Dutch Sportsman of the year. Bos's record was beaten by Frenchman Kévin Sireau at the Moscow Grand Prix on 29 May 2009 with 9.65 seconds.

On 19 April 2009, Bos was in a controversial crash in the final 800m of the final stage of the Tour of Turkey. Bos caused the crash of the eventual winner Daryl Impey by grabbing Impey's left shoulder with his right hand. Impey crashed to the left, into the barrier, next to Bos. Bos admitted pushing Impey. Bos claimed the reason for pushing Impey was because Impey was moving in on him while he was already close to the fence.[5][6][7] Bos was disqualified and fined. On 1 May 2009 the Union Cycliste Internationale (UCI) said "Bos’s behavior undermined the image, reputation and interests of cycling". Bos was charged with an infringement and was brought before a UCI disciplinary hearing in which he was found guilty of violating UCI regulations. Bos was subsequently suspended from professional racing from 15 August through 14 September 2009.

In 2012, he won the first and last stages of the Tour of Turkey. Both of these stages saw crashes in the finale, diminishing the number of sprinters Bos had to compete against.[8] Bos took the first win of his career at the World Tour level on the 2012 Eneco Tour. On Stage 3 from Riemst to Genk, he edged John Degenkolb (Argos–Shimano) on the finish line in a bunch sprint to take the victory.[9]

Bos was originally selected as a member of the Belkin squad for the 2013 Vuelta a España, however he was withdrawn before the start of the race after tests revealed he had low cortisol levels. A team statement noted that this was "an indication of sub-optimal health conditions", and that whilst low cortisol levels were not a barrier to competing in UCI World Tour races the team's medical staff and Bos had agreed to send him home.[10] Subsequently, Bos confirmed that his condition was due to an extreme reaction to asthma medication.[11]

Bos will ride for the Pro Continental team MTN–Qhubeka from 2015 until 2016.[2] Bos said about Team MTN-Qhubeka "The team has a great culture, I want to win and we will work together to win, our success is the success of Africa."[12]

""The team races for a cause that is more than just winning races and that is Qhubeka, a social initiative where they aim to put children in Africa on bicycles. I really like this human element to the team. I hope I will be able to bring a fan base with me to the team that will bring new support to the Qhubeka initiative. "

— Theo Bos

Following the Abu Dhabi Tour, where he did not finish stage 2, he has no results of any major road events since.[13]